The objective of this research was to determine whether bison (Bison bison) benefit nutritionally from feeding on areas colonized by black-tailed prairie dogs (Cynomys ludovicianus) in Wind Cave National Park (WCNP), South Dakota. I qualified differences indiet guality obtained by bison feeding on and off prairie dog towns to determine whether the superior diet quality obtained by bison on towns was sufficient to enhance their inclusive fitness. A ruminant simulation model was used to predict wieght changes based on diet qualitity of bison feeding on and off prairie dog towns. Based on simulated weight changes, I evaluated possible reproductive benefits to bision derived from feeding on prairie dog towns to various extents. Simulations indicate that typical patterns of bison use of prairie dog towns in WCNP during summer allow 5 kg of weight gain not possible for adult bison feeding solely off towns. This additional weight translates into substantial energy gain (41,650 kcal) that could account for 18% of the cost of fetal production. Typical patterns of bison use of prairie dog towns allow yearlings to gain an additional 4% of body weight compared to immature animals feeding solely off towns. This wieght gain could yield suffficient energy to allow 10 d of survival not possible for immature bison feeding solely off towns. In years of stronger selection for prairie dog towns, when simulated bison spend 70% of their feeding time on these areas, adults gained 9 kg more than those not feeding on towns. This gain could provide sufficient energy to meet 33% of fetal production costs. Immature bison feeding on prairie dog towns 70% of the time gained an additional 8% of body weight compared to those never feeding on towns, allowing for 17 more days of survival. In contrast, random use of prairie dog towns in WCNP (12%) does not appear to yield significant nutritional benefits to bison. Model output suggests that adult bison must spend at least 15-20% of their feeding time on towns from mid-June through August to realize significant nutritional benefits. This research quantifies an interspecific facilitative interaction between bison and prairie dogs under various conditions in the North American mixed-grass prairie of WCNP.